I think the reliably messing up isn't so much the lack of attention to detail, but the second point: not knowing what the standard is, why it's the standard, and why something should be done in particular way.

Definitely a you don't know what you don't know and it's hard to test safely. Done wrong, this stuff doesn't immediately blow up in your face, that happens later, usually at some future inconvenient time.

I'm still sad that I don't have debuggers, test suites, sandbox environments etc for incorporation/legal work.